台风变性加强过程的数值模拟和试验分析

Simulation on reintensification of Typhoon Winnie (1997)during extratropical transition

中文关键词:  台风，变性，重新加强，数值模拟

英文关键词:Typhoon, Extratropical transition, Reintensification, Numerical simulation

中文摘要:

      1997年登陆的Winnie台风经历了变性重新加强的过程，利用中尺度数值模式MM5对该过程进 行了数值模拟和分析。等熵位涡分析显示重新加强过程经历了2个阶段：（1）高层扰动加强期，北上的变性气旋在其高层维持了小的位涡区，使上游东移的位涡槽加强；（2）气旋斜压发展期，低层气旋上的斜压带与高层加强的扰动耦合，气旋获得斜压发展。该过程伴随着 高层风速的加强并发展为急流，这是动力平衡和低层斜压动能输送的结果。高层扰动和急流 演变过程说明了变性气旋自身对其发展的重要性。通过热带气旋分离的方法，利用数值试验 对变性气旋以及与气旋相关的物理因子的作用进行分析。结果显示，低层变性的气旋Winnie 首先通过潜热过程加强了高层的扰动，然后在其北移过程中和高层的扰动位相锁定而得到斜压发展，演变过程说明了登陆台风自身的重要性。在这个过程中，初始气旋的涡旋环流是最主要的，其次是水汽，而斜压性影响最少。斜压性影响最少是由于在气旋环流和高湿度的环境下，斜压带得到重建，使气旋仍然可以和高层的扰动相互作用而得到斜压发展。所以，斜压性仍是变性气旋再度发展的直接原因。综观台风Winnie的变性以及重新加强过程，气旋中 斜压性的产生以及维持都和与降水相关的潜热过程密切相关。

英文摘要:

      The landed typhoon Winnie (1997) on eastern China experienced a reintensificatio n process during its extratropical transition (ET). The process was numerically simulated with the mesoscale model MM5, and its evolution characteristic and phy sical mechanism were analyzed also. The analysis with isentropic potential vorti city (IPV) showed that Winnie had experienced two stages during its reintensifyi ng process: (1) Upper disturbance intensifying: in which the northward moving tr ansformed cyclone maintained a low PV in the upper level, then when the upstream PV trough moved eastward its PV gradient increased. It was shown that the uppe r disturbance had intensified. (2) Baroclinic development of transformed cyclone : in which the transformed cyclone developed when the lower baroclinic band coup led with the upper positive PV anomaly that intensified in the first stage. Simu ltaneously, during reintensification of Typhoon Winnie, the upper wind speed in creased and grew into an upper jet. It was results of the dynamical balance of t he upper disturbance and the transportation of lower baroclinic kinetic energy. The evolution of the upper disturbance and the upper jet implied that the trans formed cyclone itself might play a key role in its reintensification. By separ ating the initial cyclone, some numerical experiments to examine the effects of the transformed cyclone and its relative physical factors were performed. It was shown that the lower transformed cyclone Winnie intensified the upper disturbance at first through the latent heat process and then developed baroclinically when it moved northward, and phase locked with the intensified upper disturbance . The evolution of Winnie demonstrated the significant effect of the cyclone itself, in which, the effect of the initial cyclone circulation was the most import ant, then was the initial moisture, and the last was the initial baroclinicity. The cause for the feeble effect of baroclinicity was that the baroclinical band could be reconstructed in the circumstance of cyclone circulation and high humidity. Then the cyclone could continue to develop baroclinically when it interacte d with the upper disturbance. Thus, the baroclinicity was still the direct facto r for the transformed cyclone to reintensify. It was a special characteristic for Winnie that both the frontogenesis during transformation stage and the mainten ance of baroclinicity during reintensification stage related closely to the latent heat process accompanied with rainfall over the cyclone.